Epigenetic gene regulation through DNA methylation and histone modifications has been shown to be a crucial mechanism for the development and function of the nervous system, ranging from cell differentiation to neuronal plasticity and from learning & memory to behavior. The deregulation of the epigenome could lead to various neuropsychiatric disorders. To address the role of DNA methylation in the development and function of cortex and hippocampus, we have examined expression of DNA methyltransferases (Dnmts including Dnmt1, Dnmt3a, and Dnmt3b) in the developing and adult central nervous system (CNS). Intriguingly, we found that Dnmts such as Dnmt1 and Dnmt3a are still highly expressed in postmitotic neurons. We hypothesize that expression of Dnmts in postmitotic CNS neurons is to maintain and modulate DNA methylation patterns, which can subsequently regulate long-term changes of neuronal gene expression. To test this hypothesis, in Aim 1, we plan to generate conditional mutants with the Cre/LoxP system in which both Dnmt1 and Dnmt3a are absent in postmitotic cortical and hippocampal neurons. This unique mouse model system allows us to examine methylation changes under seizure condition in the presence or absence of both Dnmt1 and Dnmt3a. In Aim 2, we will map genome-wide methylation patterns in hippocampal dentate gyrus neurons in control and seizure conditions through shotgun bisulfate sequencing (BS-Seq) and determine the potential alteration of DNA methylation patterns in Dnmt-deficient hippocampal neurons. This BS-Seq approach has been successfully applied to decipher methylomes at single nucleotide resolution in plants and human cells. With the advent of next-generation and third generation sequencers, we would obtain methylomes in mammalian hippocampal neurons at a very reasonable cost. By mapping DNA methylation in CNS neurons under normal and seizure conditions in the presence and absence of Dnmts, we will gain insight into the role of Dnmts and DNA methylation in postmitotic neurons. Our findings will lay a solid foundation for future study to understand the involvement of abnormal methylation in neurological disorders. PUBLIC HEALTH RELEVANCE: This grant proposes to understand regulatory mechanisms of gene expression in brain cells - specifically, to examine the pattern of DNA modification (namely DNA methylation) in the DNA of nerve cells. This DNA modification is involved in the inhibition of gene expression and it is known that if DNA methylation pattern is abnormal, it can lead to human diseases including cancer and mental retardation disorders. We will use high throughput sequencing technique to identify DNA methylation patterns in the developing brain cells and examine the consequence of the perturbation of DNA methylation patterns on brain development and function, thus impacting public health by paving the way for understanding pathological mechanisms of mental retardation disorders due to the perturbation of DNA methylation.